There have been used various kinds of pipe connectors. They vary widely in structure. A typical pipe connector is shown in FIG. 1, which includes a union 17 joined to a pipe 16B by welding or soldering. A mating pipe 18A is provided with a protrusion or flange 19 formed on its leading end after a nut 18 is mounted thereon. The pipes 18A and 18B are connected by tightening the nut 18, with an O-ring inserted between union 17 and the flange 19.
However, since such conventional connector as mentioned above requires many connecting steps and one or more tools such as spanners for tightening the nut on the union, pipe connection efficiency is very low. Furthermore, since it requires a certain work space for handling the parts and the tools, it is difficult to apply the connector to the pipes to be installed in a narrow space.